1. Field of the Invention
The invention relates to an overvoltage protection element with a housing, at least one overvoltage limiting component which is located in the housing, especially a varistor, and with two connecting elements for electrical connection of the overvoltage protection element to the current path or signal path to be protected, in the normal state of the overvoltage protection element, the connecting elements each being in electrically conductive contact with one pole of the overvoltage limiting component.
2. Description of Related Art
German Patent DE 42 41 311 C2 discloses an overvoltage protection element which has a thermal disconnector for monitoring the state of a varistor. In this overvoltage protection element, the first connecting element is connected via a flexible conductor to a rigid disconnection element whose end facing away from the flexible conductor is connected via a solder point to a terminal lug provided on a varistor. The other connecting element is permanently connected to the varistor or the terminal lug on the varistor via a flexible conductor. The disconnection element is exposed to a force from a spring system which leads to the disconnection element being moved linearly away from the terminal lug when the solder connection is broken so that the varistor is electrically isolated when thermally overloaded. By way of the spring system, when the solder connection is broken, a telecommunications contact is activated at the same time so that remote monitoring of the state of the overvoltage protection element is possible.
German Utility Model DE 20 2004 006 227 U1 corresponds to U.S. Pat. No. 7,411,769 B2 discloses an overvoltage protection element in which the state of a varistor is monitored according to the principle of a temperature switch so that, when the varistor is overheated, the solder connection which is provided between the varistor and the disconnection element is broken; this leads to electrical isolation of the varistor. Moreover, when the solder connection is broken, a plastic element is pushed by the reset force of a spring out of a first position into a second position in which the disconnection element, which is made as an elastic metal tongue, is thermally and electrically isolated from the varistor by the plastic element so that an arc which may arise between the metal tongue and the contact site of the varistor is extinguished. Since the plastic element has two colored markings located next to one another, it also acts, at the same time, as a visual indicator of the state, so that the state of the overvoltage protection element can be easily read off directly on site.
German Patent DE 695 03 743 T2 corresponds to EP 0 716 493 B1 discloses an overvoltage protection element with two varistors, which has two disconnection means which can individually isolate the varistors each on their live end. The disconnection means each have one elastic disconnection tongue, the first end of the disconnection tongue being permanently connected to the first terminal and the second end of the disconnection tongue in the normal state of the overvoltage protection element being attached to a connecting tongue on the varistor by way of a solder site. If unallowable heating of the varistor occurs, this leads to melting of the solder connection. Since the disconnection tongue in the soldered-on state (normal state of the overvoltage protection element) is deflected out of its rest position and is thus pretensioned, the free end of the disconnection tongue when the solder connection softens moves away from the connecting tongue of the varistor, by which the varistor is electrically isolated. In order to ensure the required insulation and tracking resistance and to extinguish an arc which forms when the gap opens, when the disconnection tongue is pivoted, it is necessary that a distance as great as possible is achieved between the second end of the disconnection tongue and the connecting tongue of the overvoltage limiting component.
The known overvoltage protection elements are generally made as “protective plugs” which together with the bottom part of the device form an overvoltage protection device. For installation of such an overvoltage protection device which, for example, is designed to protect the phase-routing conductors and the neutral conductor, and optionally, also the ground conductor, in the known overvoltage protection devices, on the bottom part of the device, there are the corresponding terminals for the individual conductors. For simple mechanical and electrical contact-making of the lower part of the device with the respective overvoltage protection element, in the overvoltage protection element, the connecting elements are made as plug pins for which there are corresponding sockets which are connected to the terminals in the lower part of the device so that the overvoltage protection element can be easily plugged onto the bottom part of the device.
In these overvoltage protection devices, installation and mounting can be carried out very easily and in a time-saving manner due to the capacity of the overvoltage protection elements to be plugged in. In addition, these overvoltage protection devices in part still have a changeover contact as the signaler for remote indication of the state of at least one overvoltage protection element and an optical state display in the individual overvoltage protection elements. It is indicated by way of the state display whether the overvoltage limiting component which is located in the overvoltage protection element is still serviceable or not. The overvoltage limiting component here is especially varistors, but depending on the application of the overvoltage protection element gas-filled surge arresters, spark gaps or diodes can also be used.
The above described thermal isolation devices which are used in the known overvoltage protection elements and which are based on melting of a solder connection must perform several functions. In the normal state of the overvoltage protection element, i.e., in the state in which it is not disconnected, a reliable and good electrical connection between the first connecting element and the overvoltage limiting component must be ensured. When a certain boundary temperature is exceeded, the gap must ensure reliable isolation of the overvoltage limiting component and continuous insulation resistance and tracking resistance. However, the problem here is that the solder connection is continuously loaded with a shear stress as a result of the spring force of the spring element or of the disconnection tongue which has been deflected out of its rest position in the normal state of the overvoltage protection element.